Far more species may be at risk for extinction than previously estimated. According to a new study in the journal Science, the disappearance of some species will undoubtedly lead to the demise of others that rely upon them for food, shelter, pollination, and other services.

For example, the extinction of the colobus monkey may pull down three species of lice found only on this primate. Scientists led by Lian Pin Koh at the National University of Singapore and Robert Dunn at Curtin University of Technology in Perth, Western Australia, used a computer model to estimate the level of host species dependence in world food webs. They calculate that of the 12,200 species considered endangered on the International Conservation Union's Red List, at least another 6,300 are "co-endangered."

About 4,000 of the co-endangered creatures are beetles; most of the rest are butterflies, and parasites such as lice. Taking into consideration the 399 species that have already disappeared, they calculate that another 200 affiliated species probably also went extinct.

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Pollution Is Sickening Polar Bears

Polar bears may live miles from industry, but it's not far enough to escape pollution poisoning. According to a new study by Andrew Derocher, polar bears in Canada and the island of Spitzbergen in Norway show hormonal and immune system changes that correlate with the levels of pollutants in their bodies.

The scientists found that bears with the highest levels of polychlorinated biphenyls (PCBs) and pesticides also had the lowest level of antibodies in their blood. This suggests pollutants have made the bears more susceptible to infections. Reduced hormone levels could affect the bears' breeding capacity. That's particularly bad news for a species already suffering from a reduced ability to find food due to the effects of global warming.

Although neither PCBs nor the type of pesticides examined in the study are commonly produced today, they decompose very slowly. For this reason, their effects on the environment are still being revealed. The research was published in the Journal of Toxicology and Environmental Health and Environmental Health Perspectives.

Freeloaders Encouraged in Canine Society

Hungry scavengers may have driven wolves to become social animals, according to a new study. Food losses to freeloaders such as ravens, according to new research published in the journal Animal Behavior, helps explain why wolves and dogs run in packs but cats go it alone.

Juhn Vucetich of Michigan Technological University and colleagues tracked the fates of 558 moose kills by wolves in Isle Royale National Park in Michigan. Despite the wolves' best efforts, the scientists calculated wolfpacks lost between 4.4 to 81.6 pounds of food per day to ravens. Up to one-third of wolves die from starvation, so these feathered bandits pose a substantial ecological threat to wolf welfare. Though much smaller than wolves, ravens can win possession of carcasses by dint of their numbers; the scientists counted as many as 100 birds at some kills.

The researchers say that banding together helps wolves kill larger prey and spend less time shooing scavengers away. This social tendency may have made it easier for humans to domesticate dogs. By contrast, cats, coyotes, and other smaller predators tend to hunt smaller prey that they can usually finish alone and which offer little food for scavengers.

Picture a Planet

Earthlings may have gotten their first direct glimpse of a world belonging to another galaxy. Astronomers at the European Southern Observatory in Chile have announced they may have photographed an actual planet orbiting a dim star known as a brown dwarf. The pair is located about 230 light years from Earth, in the constellation Hydra.

Scientists have detected many such exoplanets in the past decade by deciphering clues such as gravitational wobbles in the paths of stars. If the reddish object in the photos does turn out to be a real planet, it will be the first seen by human eyes.

Astronomers believe the new object is likely a planet because it stays very near its star; two stars linked by gravity tend to keep farther apart. Because planets are so tiny compared to stars, viewing them across the vast reaches of space has been likened to spotting a fruit fly next to a movie spotlight.

Some Dinosaurs Were Caring Parents

A touching tableau of dinosaur family life has been unearthed in fossil beds in China. The discovery, reported in the journal Nature, offers the strongest evidence to date that dinosaurs were devoted parents.

David Varricchio of the University of Montana and colleagues have found the skeleton of an adult Psittacosaurus closely surrounded by 34 juveniles. All the dinosaurs were upright when they died, with their legs tucked underneath. This posture suggests the animals was suddenly smothered by a collapsing burrow, volcanic eruption, or flood.

Birds, considered the modern-day descendants of dinosaurs, are famous for tending their nests and caring for helpless young. But relatively few fossils of dinosaur families have survived, making scientists hesitant to claim these terrible lizards provided much more than cursory child care. Psittacosaurs were plant-eaters that grew to about the size of a dog. They had parrotlike beaks, could stand up to feed on tall shrubs, and lived about 119 to 97.5 million years ago.

Great Ocean Once Wet Mars

Though bone-dry today, Mars once held an ocean containing more water than all of North America's Great Lakes put together. Such a large body of water, scientists report in the journal Nature, may have warmed the planet's climate enough to support life.

The evidence was gathered by the Mars Odyssey spacecraft, which has been orbiting the Red Planet for the last three years. Using an instrument designed to measure soil particle sizes, the satellite spotted layers of sediments characteristic of those left by a large body of water. The layers are at least one-third of a mile thick, suggesting the ocean must have been quite deep. The area studied overlaps with terrain explored in more detail by the rover Opportunity.

The rover, which landed on Mars' Meridiani Planum plain, has identified sulfur and gray hematite deposits thought to have formed under water. The presence of these minerals also suggest the water would have been salty. The Odyssey satellite has found gray hematite formations over a much wider area, suggesting the ocean once covered at least 127,000 square miles but was probably much larger. Scientists estimate the ocean existed about 3.7 billion years ago.